Treatment of nickel for electroplating chromium thereon



United States Patent TREATMENT OF NICKEL FOR ELECTROPLATEN G CHROM'IUMTHEREON James D. Patrick, Dayton, Ohio, assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware No Drawing.Application October 6, 1955 Serial No. 539,000

2 Claims. (Cl. 204-440) This invention relates to the preparation ofnickel for electroplating chromium thereon.

In commercial processes of plating chromium on nickel it is commonpractice to activate the nickel surface prior to chromium plating bycleaning the article in a solution of hydrochloric or sulphuric acid.The article or part may be merely dipped in an aqueous solution ofeither of these acids or the part being treated may be made cathodic inthe solution. Normal time in the acid solution is quite short and if theparts remain in the activated solution too long unsatisfactory chromiumplate results, thus making it necessary to remove the chromium plate andreplate the parts. In the operation of automatic plating machines whichare commonly used today the machine may be frequently stopped withoutwarning and in case the parts are left too long in the activatingsolution defective chromium plating will result such that it will benecessary to reject the articles. Accordingly the primary object of thisinvention is to provide an improved procedure for activating nickel forelectrodepositing chromium thereon and especially an activatingprocedure in which prolonged immersion in the activating solution willnot adversely affect the parts being processed.

The present invention provides an improved activating process andimproved electrolytes for carrying out the process. The improvedelectrolytes employed in accordance with the invention comprise aqueoussolutions of chromic acid together with minor proportions of other ions,such as sulfate, chloride, fluoride, silicouoride or fluosilicate ions.These ions may be added as acids or as salts, for example, alkali metalor alkaline earth metal salts. The nickel surface to be treated, whichmay be a nickel article or a composite article comprising a base memberon which is a coating of nickel, is immersed in the solution andelectric current is applied with the nickel or nickel coated article thecathode. A preferred bath comprises 2 to 6 oz./gal. of chromic acid andfrom .10 to .15 oz./gal. of sulfate added as sulphuric acid. While theseare the preferred concentrations considerable variation may be employedwith satisfactory results. For example, the chromic acid may range from1 to oz./gal. and the sulfate from .05 to .30 oz./gal. When other ionssuch as chloride, fluoride, silico-fluoride, or fiuosilicate are used inplace of sulfate equivalent amounts are used.

The nickel surface to be activated is employed as a cathode in theelectrolyte. The anodes may be of any suitable material. Lead and leadalloy anodes are quite satisfactory. A voltage on the order of 3 to 4 ispreferred for best results although satisfactory results may be obtainedwith other voltages, for example, those on the order of 2 to 6. Anaverage current density of 5 a. s. f. is satisfactory under mostconditions. The cut- 2,836,552 iatented May 27, 1958 ice rent densityshould be kept below that at which metallic chromium will be depositedor cloudy chromium deposits will be produced during the subsequentchromium plat ing operation. In view of the fact that chromium may startto deposit at about 40 a. s. f. under certain combinations of the abovevariables, average current densities of about 10 a. s. f are about ashigh as it is safe to go on most complicated shapes; otherwise thecurrent density on some areas being treated may exceed 40 a. s. f. Forthese reasons the preferred amperage is on the average of 4 to 6 persquare foot, although the range of 2 to 12 is satisfactory under mostconditions.

Optimum results have been obtained with bath temperatures on the orderof to F. However, considerable variation is permissible and temperatureranges on the order of 60 to F. are satisfactory.

Optimum results are obtained with electrolyzing times of 30 seconds tothree minutes. Under some conditions, as when the nickel surface isalready fairly active as it enters the bath, shorter times of only about10 to 15 seconds may be employed. Longer times than three minutes mayalso be used. One important advantage of the present invention is thatthe parts may be left in the bath for prolonged periods up to 30 minutesor more.

After the activating treatment the parts may be plated with chromium byknown procedures in any conventional or other chromium plating bath.

Various changes and modifications may be made in the embodiments of myinvention described herein without departing from the principles andspirit of the invention.

I claim:

1. A method of activating a surface of nickel for the electrodepositionof chromium thereon which comprises providing an aqueous solutionconsisting essentially of chromic acid Within the range of 2 to 6 ouncesper gallon and sulfate within the range of .05 to .30 ounce per gallon,immersing the nickel in said solution, said solution being at atemperature within the range of about 60 to 160 F., and passing anelectric current through said solution with the nickel as the cathode ata current density of about 2 to 12 amperes per square foot for a timewithin the range of about 30 seconds to three minutes.

2. A process of activating a surface of nickel for the electrodepositionof chromium thereon which comprises providing an aqueous solutionconsisting essentially of chromic acid within the range of 2 to 6 ouncesper gallon and sulfate within the range of .10 to .15 ounce per gallon,said solution being at a temperature within the range of 80 to 130 F.,immersing the nickel in said solution, and passing an electric currentthrough the solution with the nickel as cathode at a current density ofabout 4 to 6 amperes per square foot for a time within the range of 30seconds to three minutes.

References Cited in the file of this patent UNITED STATES PATENTS1,827,247 Mason Oct. 13, 1931 2,182,244 Beall Dec. 5, 1939 FOREIGNPATENTS 255,421 Switzerland Jan. 17, 1949 OTHER REFERENCES Principles ofElectroplating and Electroforming, Blum and Hogaboom (1949), publ. byMcGraw-Hill Book (30., pp. 338-343 cited.

1. A METHOD OF ACTIVATING A SURFACE OF NICKEL FOR THE ELECTRODEPOSITION OF CHROMIUM THEREON WHICH COMPRISES PROVIDING AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF CHROMIC ACID WITHIN THE RANGE OF 2 TO 6 OUNCES PER GALLON AND SULFATE WITHIN THE RANGE OF .05 TO .30 OUNCE PER GALLON, IMMERSING THE NICKEL IN SAID SOLUTION, SAID SOLUTION BEING AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 60* TO 160*F., AND PASSING AN ELECTRIC CURRENT THROUGH SAID SOLUTION WITH THE NICKEL AS THE CATHODE AT A CURRENT DENSITY OF ABOUT 2 TO 12 AMPERES PER SQUARE FOOT FOR A TIME WITHIN THE RANGE OF ABOUT 30 SECONDS TO THREE MINUTES. 